Optical encoders are used to monitor the motion of, for example, a shaft such as a crank shaft. Optical encoders can monitor the motion of a shaft in terms of position and/or number of revolutions of the shaft. Optical encoders typically use a codewheel attached to the shaft to modulate light as the shaft and the codewheel rotate. The light is modulated as it passes through a track on the codewheel that includes a pattern of transparent and opaque sections. As the light is modulated in response to the rotation of the codewheel, a stream of electrical signals is generated from a photodetector array that receives the modulated light. The electrical signals are used to determine the position and/or number of revolutions of the shaft.
Separate position and index tracks on the codewheel are used to determine position and number of revolutions. The position and index tracks must be precisely aligned with the corresponding position and index track photodetector arrays to achieve reliable results. Because each track must be aligned with its corresponding photodetector array, the task of alignment becomes more difficult as the number of tracks increases. Further, some applications of optical position encoders demand higher resolution position information, which requires smaller tracks and photodetector arrays. Smaller tracks and photodetector arrays add additional challenges to the task of alignment.